Construction of lens barrel operated by electromagnetic induction

ABSTRACT

A lens assembly including an adjusting mechanism arranged to render a part or parts of or all of the optical elements, constituting an optical system, movable by an electric motor drive arrangement, the lens barrel is composed of a stator or stators of one or a plurality of linear motors for driving the adjusting mechanism. The movable element of the linear motor corresponding with the stator is formed into a hollow space, in which each of the movable optical elements can be accommodated.

This is a continuation of application Ser. No. 396,030 now U.S. Pat. No.4,534,624, filed July 7, 1982.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a photography lens which is adapted forimaging an object to be photographed and is capable of adjusting themagnification of a picture image.

2. Description of the Prior Art

The conventional lens of this type has been arranged as follows: Theimage of an object to be photographed is captured by a focusing lensgroup of the photograph taking lens. Then, within a cylindrical lensbarrel, the focusing lens group is moved in the direction of the opticalaxis of the lens to adjust it to an in-focus position. In a photographtaking lens of this type, a focusing lens group is mounted on the lensbarrel which is either fixedly attached to a camera or arranged to beattachable to and detachable from the camera through suitable couplingmeans such as a bayonet mount. A focusing ring is mounted on the outsideof the lens barrel. Between the focusing ring and the lens holder ismeans for transmitting a rotatory motion and for converting it into alinear motion in the direction of the optical axis of the lens, such asa helicoidal mechanism. With this arrangement provided, a focusingoperation is performed by adjusting the movement of the lens holderthrough an operation to rotate the focusing ring around the opticalaxis.

Devices called automatic focusing devices have been developed and haverecently come to be used for cameras. The automatic focusing devices ofthe prior art are arranged to adjust the position of a focusing lensgroup by automatically moving it upon detection of the position of anobject to be photographed. These automatic focusing devices includevaried types such as the type using the principle of trigonometricalmeasurement, the contrast type utilizing the contrast of the image of anobject formed on an imaging plane (or at a position equivalent to theimaging plane), etc. Most interchangeable lenses for single-lens reflexcameras are of the contrast type.

There have been proposed single-lens reflex cameras incorporating suchautomatic focusing devices with interchangeable lenses having suchautomatic focusing devices disposed within their lens barrels. Typicalexamples of these single-lens reflex cameras and interchangeable lenseshave been disclosed, for example, in pending U.S. patent applicationSer. No. 280,549, filed July 6, 1981, U.S. Pat. No. 3,972,056, etc.

In accordance with the arrangement of the prior art, a driving devicefor driving a lens holder of a lens barrel in response to a signal froman automatic focusing device is comprised of a motor for driving thelens holder in response to an automatic focusing signal, and a gearmechanism for transmitting the rotating force of the motor to the lensholder. However, since the components of the lens barrel are arrangedseparately from the motor and the gear mechanism components, thearrangement of the prior art results in numerous parts and manyconnection parts between one unit and another. This has presentedproblems in terms of the cost and difficulty of assembly and adjustmentwork.

U.S. Pat. No. 4,152,060, entitled "Epicyclic ElectromechanicallyActuated Lens Drive", discloses a device in which the stator element andthe movable element of an electromagnetic induction mechanism arefunctionally incorporated within a lens barrel; and a lens holder whichcarries a focusing lens group is arranged to be driven and controlledalong the optical axis by virtue of electromagnetic induction. In thiscase, the lens holder is rotatably attached to the inside of acylindrical armature while a stator is arranged coaxially with theoptical axis of the lens. The armature and the lens holder are connectedto each other by a mechanical coupling. A stepwise rotatory motion of arotating device is converted into a stepwise focusing movement of thelens holder which takes place along the optical axis. The mechanicalcoupling is effected through engagement of the gear teeth of the lensholder and the armature. In the device according to U.S. Pat. No.4,152,060, the driving force on the lens holder in the optical directionmust be obtained by converting the rotatory motion performed by thestator and the armature into a linear motion, resulting from the geartooth coupling. This arrangement tends to have a loss in the efficiencyof the driving force transmission. Besides, the use of an epicyclicmotor also requires a high degree of precision in machine work on theparts involved in gear tooth coupling between the armature and the lensholder. It is a further shortcoming of this device that back-lash in thegear tooth coupling part causes some error in the movement of the lensholder and this problem also calls for a solution.

Further, in the field of zoom lenses which are arranged to vary themagnification of the picture image of an object to be photographed,lenses arranged to accomplish a position control over a variator lensgroup and a compensator lens by an electrical process are known, forexample, U.S. Pat. Nos. 4,161,756 and 3,884,555, etc. The driving forcefor the lens holders of these variator and compensator lenses isarranged to be transmitted from a motor through a gear train mechanism.Therefore, the lens drive mechanism of these patents is clumsy orunshapely and has shortcomings with respect to the cost and assembly andadjustment work in the same way as in the case of the focusing lensarrangement mentioned in the foregoing.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide a lens barrelwhich eliminates the above-stated shortcomings of the device of theprior art. In other words, the objects include:

(1) Allowing a broader design latitude for the shape of the lens barrelto avoid a clumsy appearance. To attain this object, the use of themotor which has conventionally been used for the peripheral gear and thereduction mechanism of distance adjusting and zooming rings is rescindedand the same function is performed by a lens barrel which is arranged toperform the motor function.

(2) Having a plurality of driving actions for zooming, focusing, etc.,performed within the same lens barrel. Unlike the conventional method,this is accomplished by arranging the lens barrel so it serves as alinear step motor while also performing the functions of a lens barrel.This arrangement lessens wasteful use of space because a motor which hasno reduction mechanism can be directly connected to accomplish drivingactions for zooming and focusing.

(3) To make the speed variable over a wide range, from a low to a highspeed. Unlike the conventional method, a movable element is arranged totravel at speeds which vary over a wide range, from a low to a highspeed, in proportion to the frequency of the pulse signal of a drivecontrol circuit connected to a motor to attain the above-stated objects(1), (2) and (3) of the invention. In addition to the variable speedarrangement, the movable element can be kept in a stopped position byits own retentivity without having recourse to a brake.

(4) To permit the lens barrel to utilize a standardized mount formounting and dismounting it to and from a camera without difficulty.

The above-stated problems, encountered by the conventional lens barrels,are thus eliminated by replacing the conventional arrangement of adriving motor and a reduction mechanism within the camera system withthe above-stated linear motion which is also arranged to serve as a lensbarrel in accordance with the invention.

It is a further object of the invention to provide a lens barrelconstruction wherein the stator element and the movable element of astepping motor, which has been known in the field of motors, arefunctionally arranged as a fixed part and a moving part of the lensbarrel and a focusing lens is arranged to be movable by anelectromagnetic induction mechanism. In particular, the lens barrelconstruction according to the invention obviates the necessity of anyelicyclic gear coupling between an armature and a lens holder such asthe one disclosed in the above-stated U.S. Pat. No. 4,152,060.

These and further objects, features and advantages of the invention willbecome apparent from the following detailed description of preferredembodiments thereof taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a lens barrel as an embodimentof the present invention.

FIGS. 2(a), (b), (c) and (d) are detailed views showing the operation ofa linear step motor which forms the first moving ring of the lens barrelshown in FIG. 1. These views show that a movable element movesaccordingly as a stator element is gradually excited.

FIGS. 3(a), (b), (c) and (d) are detailed views showing the operation ofa linear step motor forming a second moving ring of the lens barrelshown in FIG. 1.

FIGS. 4(a), (b), (c) and (d) are detailed views showing the operation ofa linear step motor forming a third moving ring of the lens barrel shownin FIG. 1. In these drawings, FIGS. 3 and 4, the movement of a movableelement is illustrated by steps in the same manner as in FIG. 2.

FIG. 5 is a circuit diagram showing means for minimizing currentconsumption where the movable element of the lens barrel is arranged toa large amount.

FIGS. 6, 7 and 8 illustrate a second embodiment of the invention. Ofthese drawings, FIG. 6 is a cross-sectional view taken in the axialdirection of the embodiment; FIG. 7 is a partial cutaway view showingthe essential parts of a stator element and a movable element arrangedto electromagnetically drive a lens holding member shown in FIG. 6; andFIG. 8 is a sectional view taken along line A1-A2 of FIG. 6, showing therelation of teeth of a stator to those of a rotor and the arrangement ofwindings (in the case of five-phase excitation).

DESCRIPTION OF PREFERRED EMBODIMENTS

A first embodiment of the present invention is as shown in FIGS. 1through 5. FIG. 1 is a sectional view of a zoom lens using a linear stepmotor arranged to serve as the lens barrel in accordance with theinvention. The embodiment includes a front lens barrel 101; a middlelens barrel 102; and a rear lens barrel 103. The front lens barrel 101and the middle lens barrel 102 are connected by a connection member 104while the middle lens barrel 102 and the rear lens barrel 103 areconnected by a connection member 105 to form one unified base cylinder.There are arranged, along the optical axis 0₁ -0₂ (within this basecylinder, and starting from the object side of the zoom lens), a frontlens group consisting of lenses L1, L2 and L3; a variator lens groupconsisting of lenses L4, L5 and L6; a compensator lens group L7; and afocusing lens group consisting of lenses L8, L9, L10, L11 and L12. Thefront lens group L1, L2 and L3 are fixedly positioned within the lensbarrel 101 and do not participate in the focusing operation. Thevariator lens group (L4, L5 and L6) is positioned within a lenscontaining part 106a of a lens barrel 106. The compensator lens group L7is positioned within a lens containing part 107a of lens barrel 107.

Two pairs of linear step motors which also serve as lens barrels inaccordance with the present invention are composed of the lens barrel102 forming the above-stated base cylinder, the lens barrel 106containing the variator lens group L4, L5 and L6 and the lens barrel 107containing the compensator lens group L7.

A part of the lens barrel 102 is arranged to serve as the stator 108 ofthe upper linear step motor, as viewed on the drawing. This stator 108comprises a permanent magnet 201 and ferromagnetic members 202 and 203each having a plurality of divided teeth. Each of these ferromagneticmembers is provided with a coil which is wound around it and isconnected to a motor drive circuit. A movable element which will bedescribed later is arranged to be moved by a magnetic field produced atthe coil by the action of the motor drive circuit. Another part of thelens barrel 102 is also arranged to serve as the stator 121 of the lowerlinear step motor, as viewed on the drawing, in the same manner as theother part serving as the upper linear step motor. The stator 121comprises a permanent magnet and ferromagnetic members each having aplurality of divided teeth. The ferromagnetic member has a coil woundaround it while the coil is connected to the motor drive circuit. Amagnetic field is to be produced there to move a movable element by theaction of the motor drive circuit. The lens barrel 106 has aferromagnetic movable element 136 attached thereto in a position toconfront the above-stated stator 108. A metal piece 138 is also attachedto the lens barrel 106. The lens barrel 107 likewise has a ferromagneticmovable element 137 attached thereto in a position to confront thestator 121 and has a metal piece 139 also attached thereto. Each ofthese movable elements is provided with a plurality of divided teeth.Guide shafts 142 and 143 which are arranged in parallel with the opticalaxis 0₁ -0₂ are interposed in-between and secured to part 140 whichprotrudes to a position not affecting an effective picture plane withinthe lens barrel 102 and a holding plate 141 which is attached to thelens barrel. The lens barrels 106 and 107 are arranged to be slidableand are guided on shafts 142 and 143. The metal piece 138, attached tothe lens barrel 106, which contains the variator lens group L4, L5 andL6, is fitted on the guide shaft 142 and is arranged to be slidablethereon along the optical axis 0₁ -0₂. These parts constitute a firstmovable ring. The other metal piece 138, which is attached to the lensbarrel 107 containing the compensator lens group L7, is likewise fittedon the other guide shaft 143 and is also arranged to be smoothlyslidable thereon in the direction of the optical axis 0₁ -0₂. Thoseparts constitute a second movable ring.

The first movable rings 106 and 138 and the second movable rings 107 and138 are connected to the motor drive circuit and a motor control signalcircuit through the coil of the stator (which is also arranged to serveas the lens barrel 102) and connection terminals which are not shown.The motor control signal circuit is designed to actuate the motor with apulse signal produced therefrom. To adjust the zoom magnification to adesired value the linear step motor, according to the invention, isactuated to vary the magnification by moving the first movable ring.However, it is impossible to keep the air space distance between thelens L6 of the variator lens group and the compensator lens L7 unchangedat every value of magnification. Because the aberration and the in-focuspoint varies with the zooming magnification, this prevents obtaining asharp picture. To solve this problem, therefore, the air space distanceis varied by moving the compensator lens L7 within the second movablering. Since such distances are known at the time of designing the lens,the values of these distances are stored in the motor control circuit.When the zoom magnification is varied with the above-stated movablering, which ring slides from the wide angle side to the telephoto sideand vice versa, the focus is corrected by the automatic operation of themotor which moves the second movable ring in accordance withinstructions from the motor control circuit. Meanwhile, a pair of linearstep motors of this embodiment are formed by the lens barrel 103 whichconstitutes the base cylinder and a lens barrel 150 which contains thefocusing lens group L8-L12. Stators 144 and 145, which are made of aferromagnetic material and are respectively provided with a plurality ofteeth protruding upward and downward, are attached to parts of theinside of the lens barrel 103 as shown in the drawing. Further, movableelements 146 and 147 are attached to the outer circumference of thefocusing lens barrel 150 and are arranged to confront, respectively, thestators 144 and 145. Each of the movable elements 146 and 147 comprisesa permanent magnet and a ferromagnetic member having a plurality ofdivided teeth. A coil is wound around each of the ferromagnetic membersand is connected to the motor drive circuit. With this coil arrangement,a magnetic field is produced by the action of the drive circuit to moveeach of the movable elements. Two ends 155 and 156 of the focusing lensbarrel 150 are fitted on the two inner parts 153 and 154 of the lensbarrel 103 at their fitting parts 155a and 156a. The lens barrel 150which is formed into one body with the movable elements is thus arrangedto be smoothly movable. When a magnetic field is produced at the movableelement by the switching actions of the motor drive and control circuit,the focusing lens barrel 150 smoothly slides, together with the lensesL8-L12, along the optical axis 0₁ -0₂ to perform a focusing operation.The camera is provided with a detection element which is not shown butis disposed on the imaging plane 159 or in a conjugate positionequivalent to the imaging plane and is arranged to detect the degree ofdefocus on the imaging plane. With the detection element arranged toproduce a signal, there also is provided a display device which iscapable of taking out and amplifying the signal and is arranged todiscern a near or a far focus and the extent of deviation of it from anin-focus point. The switches of the motor drive circuit and the motorcontrol circuit are switched on and off, between advancing andretracting positions, according to the display device, in order toaccomplish the correct focusing operation. A pulse signal producedthrough the above-stated motor drive and control circuits causes themovable element, which serves also as the focusing lens barrel, to slideforward and backward until it comes to an in-focus position.

The lens unit is coupled with a camera body by means of a mount screw157. The lens coupling plane and the imaging plane 159 are spaced at aprescribed distance l1. The mount screw 157 is fitted on the peripheralpart 103' of the lens barrel 103 and is secured thereto by means offixing member 158. In cases where the index position of the lens unitmust be changed relative to the camera body, the index position can beadjusted as desired by loosening the fixed member 158, and then freelyturning the mount screw 157 and the lens unit relative to each other,and tightening the fixing member 158 to fix the mount screw 157.

The details of the operation of the movable element and the stator inthe linear step motor, related to the first movable ring shown in FIG.1, are as shown in FIG. 2. The following description covers theoperation of them when the linear step motor is used as drive source.Referring to FIG. 2, permanent magnets 202 and 203 which are attached tobase cylinder 102 are made of a ferromagnetic material and are composedof magnetic poles 1, 2, 3 and 4 and coils. The coils are provided withpower supply closing parts 204 and 205 for the purpose of exciting them.Movable element 136 which is attached to lens barrel 106 consists of aplurality of teeth 206 and forms the first movable ring.

When the coils are excited one after another, the movable element movesin a manner as shown in FIGS. 2(a)-(d). Under the condition shown inFIG. 2(a), current is supplied to point 204 while point 205 remainsunexcited. At coil 202, a magnetic flux from the permanent magnet entersteeth D and F through poles 3 and 4. Poles 3 - tooth D and pole 4 -tooth F are magnetically balanced.

Meanwhile, at the other coil 1, the magnetic flux produced by thepermanent magnet and another magnetic flux produced by a coil currentare added up and concentrated at tooth A. On the other hand, at coil 2,the magnetic flux produced by the permanent magnet and the magnetic fluxproduced by the coil current are offset by each other and the resultantflux becomes zero. Accordingly, the magnetic flux forms a closed loopthrough pole 1→tooth A→teeth D and F→and poles 3 and 4. Therefore, pole1 and tooth A are balanced in the most magnetically stable position.Following this, coil 205 is excited and a sum of the magnetic fluxproduced by the permanent magnet and the coil current is concentrated atpole 4. At pole 3, the magnetic fluxes produced by the permanent magnetand the coil current are offset by each other resulting in zero magneticflux there. Meanwhile, the magnetic flux produced by the permanentmagnet is concentrated at the teeth A and C, since the poles 1 and 2 arenot excited. As a result, the magnetic flux forms a closed loop of pole4→and tooth F→teeth A and C→poles 1 and 2. Accordingly, the magneticflux density is concentrated between pole 4 and the tooth F. This causesthe movable element to move to the left, as much as 1/4 pitch of thetooth arrangement as shown in FIG. 2(b).

Next, coil 204 is excited as shown in FIG. 2(c) and the sum of magneticflux produced by the permanent magnet and the magnetic flux produced bythe coil current concentrate at pole 2. At pole 1 the magnetic fluxesproduced by the permanent magnet and the coil current mutually negateeach other leaving no magnetic flux there. Since poles 3 and 4 are notexcited, the magnetic flux produced from the permanent magnet isdistributed through poles 3 and 4. Accordingly, the magnetic fluxconcentrates at pole 2 and tooth C to cause the movable element again tomove to the left, as indicated by an arrow, as much as 1/4 pitch. FIG.2(d) shows the condition which results when coil 205 is excited underthe condition shown in FIG. 2(c). In this case, the magnetic fluxconcentrates in pole 3 as previously mentioned. The movable element thenagain moves as much as 1/4 pitch in the direction of the arrow as shownin FIG. 2(d). The movable element then moves to the left to the extentof one pitch when the coils are excited one after another, as shown inFIGS. 2(a)-(d). While FIGS. 2(a)-(d) show the leftward movement of themovable element, the movable element can be moved to the right bychanging the excitation sequence to a sequence of steps different thanthose in FIG. 2(a)→(d)→(c)→(b). Thus, the direction of the movableelements motion can be determined by shifting the sequence of theexciting steps.

The operation of the movable element and the stator of the linear stepmotor related to the second movable ring shown in FIG. 1 is as shown indetail in FIG. 3. The linear step motor includes a permanent magnet 301attached to base cylinder 102 and ferromagnetic members 302 and 303which consist of poles 1, 2, 3 and 4, and coils forming magnet parts.There are provided power supply parts 304 and 305. Movable element 137,which is attached to lens barrel 107 and is made of a ferromagneticmaterial, consists of a plurality of teeth 306. These parts constitutethe second movable ring.

The movable element is moved by exciting the coils one after another inthe manner shown in FIGS. 3(a)-(d). Under the condition shown in FIG.3(a), coil 304 is excited. In the meantime, coil 305 remains unexcited.At magnet part 302, a magnetic flux produced by the permanent magnetenters teeth D and F through poles 3 and 4. Pole 3 - tooth D and pole4 - tooth F are magnetically balanced. Meanwhile, at pole 1, a magneticflux produced by the permanent magnet and another magnetic flux producedby a coil current are added up and the sum of the magnetic fluxesconcentrates at tooth A. At another pole 2, the magnetic flux producedby the permanent magnet and the magnetic flux produced by the coilcurrent negate each other leaving no magnetic flux there. Accordingly, aclosed loop of magnetic flux is formed through pole 1→tooth A→teeth Dand F→poles 3 and 4. Pole 1 and tooth A are thus balancing inmagnetically stable positions. Following that, coil 305 is excited, asshown in FIG. 3(b), and the magnetic fluxes produced by the permanentmagnet and the coil current are summed up and applied to pole 4.Meanwhile, the magnetic fluxes produced by the permanent magnet and thecoil current are oppositely applied to pole 3. As a result, no magneticflux remains at pole 3. On the other hand, since poles 1 and 2 areunexcited, the magnetic flux produced by the permanent magnetconcentrates at teeth A and C. A closed loop of magnetic flux is formedthrough pole 4→tooth F→teeth A and C→poles 1 and 2. As a result, themagnetic flux density is concentrated between pole 4 and tooth F therebymoving the movable element as much as 1/4 pitch of the tooth arrangementin the direction of the arrow.

When current is passed through coil 304 as shown in FIG. 3(c), the sumof the magnetic flux produced by the magnet and the magnetic fluxproduced by the coil current concentrates at pole 2. At pole 1, themagnetic fluxes produced by the permanent magnet and the coil currentnegate each other leaving no magnetic flux there. Since poles 3 and 4are not excited, the magnetic flux from the permanent magnet isdistributed through poles 3 and 4. Thus, the magnetic flux concentratesat pole 2 and tooth C. As a result, the movable element again moves asmuch as 1/4 pitch to the right as indicated by an arrow. Under thiscondition, when coil 305 is excited, there exists a condition as shownin FIG. 3(d). Under the condition shown in FIG. 3(d), the magnetic fluxconcentrates at pole 3 again causing the movable element to move to theextent of 1/4 pitch in the direction of the arrow. With the coilsexcited one after another in the sequence of steps, as shown in FIGS.3(a)-(d), the movable element moves to the right to a total extent ofone pitch.

While the rightward movement of the suitable element takes place asshown in FIGS. 3(a)-(d), the movable element can be moved to the left bychanging the sequence of the steps of FIG. 3 to another sequence FIG.3(a)→(d)→(c)→(b). Therefore, the moving direction of the movable elementis determined by the sequence of excitation of the coils.

The details of the operation of the movable element and stator of thelinear step motor relative to the focusing lens barrel which is shown inFIG. 1 are as shown in FIG. 4. Referring to FIGS. 4(a)-(d), this linearstep motor includes a permanent magnet 401 which is attached to thefocusing lens barrel 150; and magnet parts 402 and 403 which are made ofa ferromagnetic material and consists of poles 1, 2, 3 and 4 and coils.These coils are arranged to be excited through power supply closingparts 404 and 405. Unlike the preceding cases of FIGS. 2 and 3, theseparts 404 and 405 are arranged to serve as movable element. Aferromagnetic member 406 which is attached to base cylinder 103 consistsof a plurality of teeth.

The steps of exciting these coils to move the movable element will beunderstood from the following description with reference to FIGS.4(a)-(d). Under the condition shown in FIG. 4(a), excitation is effectedthrough part 404 while part 405 remains unexcited. At magnet part 402,the magnetic flux from the permanent magnet enters teeth D and F throughpoles 3 and 4. Poles 3 - tooth D and pole 4 - tooth F are magneticallybalanced. In the meantime, magnetic fluxes produced by the permanentmagnet and a coil current are summed up and the sum of magnetic fluxesconcentrates at the tooth A. At pole 2, the magnetic fluxes produced bythe permanent magnet and the coil current negate each other leaving nomagnetic flux there. Accordingly, the magnetic flux forms a closed loopthrough pole 1→tooth A→teeth D and F→and poles 3 and 4. Accordingly,pole 1 and tooth A are balanced in magnetically stable positions.Following that, when part 405 is excited as shown in FIG. 4(b), the sumof the magnetic fluxes produced by the permanent magnet and the coilcurrent is applied to and is concentrated at pole 4. Meanwhile, themagnetic fluxes produced by the permanent magnet and the coil currentnegate each other leaving no magnetic flux there. At poles 1 and 2, themagnetic flux produced by the permanent magnet concentrates at teeth Aand C and the magnetic flux forms a closed loop through the pole 4 -tooth F - teeth A and C - and poles 1 and 2 because poles 1 and 2 arenot excited. As a result, the movable element moves to the left as shownby an arrow to an extent as much as 1/4 pitch of the tooth arrangementas shown in FIG. 4(b).

Next, when excitation is effected through part 404 as shown in FIG.4(c). The magnetic flux produced by the permanent magnet and themagnetic flux produced by the coil current are summed up and the sumconcentrates at pole 2 while the magnetic fluxes produced by thepermanent magnet and the coil current mutually negate leaving nomagnetic flux at pole 1. Since poles 3 and 4 are not excited, themagnetic flux from the permanent magnet is distributed through thesepoles. Accordingly, the magnetic flux concentrates at pole 2 and tooth Ccausing the movable element to move again to the left as indicated by anarrow as much as 1/4 pitch. After that, when excitation is effectedthrough the part 405 as shown in FIG. 4(d), the magnetic fluxconcentrates at pole 3 in the same manner as mentioned above.Accordingly, the movable element is caused to move again to the left inthe direction of the arrow as much as 1/4 pitch. Therefore, the movableelement is caused to move to the left to an extent of one pitch by theabove-stated stepwise direction as shown in FIGS. 4(a) through 4(d). Themovable element can be moved in the reverse direction, that is, to theright, by effecting the stepwise excitation in a sequence of stepscorresponding to FIG. 4(a)→(d)→(c)→(b).

The arrangements shown in FIGS. 2, 3 and 4 are applicable to a lensbarrel wherein the movable elements are not required to be moved to agreat extent. However, in cases where the movable elements must be movedto a greater extent or stroke, the embodiment must be arranged as shownin FIG. 5. In this case, a plurality of coil units 504, 505, n₁ ---n_(n) which correspond to parts 202 and 203 shown in FIG. 2 (consistingof a permanent magnet, ferromagnetic members and exciting coils) arearranged in a row. A movable element 506 is arranged to be moved inclose contact with these coil units. This arrangement gives a relativelylong stroke. Since, however, it is not desirable, in terms ofefficiency, to always allow a current to flow simultaneously to all thecoil units 504, 505, n₁, n₂, --- n_(n), the current is allowed to flowonly to the coil that is confronting the movable element; in theparticular example shown in FIG. 5, coil 504. More specifically, thereis provided a changeover device 503, which shifts the current supplyfrom one coil unit to another as necesary. This is one example of apower saving excitation method. In FIG. 5, reference numeral 501indicates an input terminal for a coil current control signal. Timing ofthe current supply changeover by the changeover device 503 can beaccomplished by employing command pulses which permit computation ofextent of the movement (for an open loop) in effecting current supplychangeover between the coil units 504, 505, n₁, n₂, --- n_(n), becausethe motor is a step motor.

It is also possible to move a movable element 507 (indicated by a brokenline) and another movable element 506 independently of each other bydividing the coil units 504, 505, n₁, n₂, ---, n_(n) into two groups andby carrying out phase excitation control over each group independently.Further, since the method of dividing the coil units 504, 505, n₁, n₂,---, n_(n) into a plurality of groups to carry out phase excitationcontrol over one group independently, permits one of the same number ofcorresponding movable elements to be moved independently of anothermovable element, a plurality of movable elements can be arranged intoone package using one common stator. Such an arrangement permitsconstruction of a compact linear pulse motor.

The zoom lens which is arranged in the manner as described in theforegoing is mounted on a camera and is directed to an object to bephotographed. Then, trimming is carried out at a desired magnificationto effect focusing on an imaging plane with a high degree of resolutionafter aiming at an image of the object located at a certain distancewithin a photographing visual field. The operation of the zoom lenswhich is arranged as described in the foregoing is as follows: The zoomlens unit is first mounted on the camera. The zoom lens is directed toan object to be photographed. Next, to bring the image of the object toa desired size, the switch of a zooming button connected to a motordrive circuit is operated. With the switch closed, the coils connectedto the motor drive circuit and the control circuit are excited in thesequence shown in FIG. 2 causing the first movable ring together withthe variator lenses L4-L6 to slide along the guide shaft 142 in thedirection of the optical axis 0₁ -0₂, so that the size of the image ofthe object can be varied to a desired size. At this time, the secondmovable ring also moves following the movement of the first movablering. This is because the desired distance between the first and secondmovable rings is stored in the control circuit. The coils connected tothe motor drive circuit and the control circuit cause the second movablering and the compensator lens to move in accordance with the commandfrom the control circuit, as shown in FIG. 3, in the direction of theoptical axis 0₁ -0₂ while being guided by guide shaft 143. The slidingmovement of the second movable ring completely eliminates any adverseeffect of the zooming action on the focused state of the image onimaging plane 159. Following this, when the image of the object isadjusted to a distance measurement mark provided within a viewfinder, adefocused degree detecting device indicates whether the image is nearfocused or far focused. Next, when a button switch connected to thefocusing motor drive circuit is operated, the coils connected to themotor drive circuit and the control circuit cause lens barrel 150 andfocusing lens L8-L12 to move along the optical axis 0₁ -0₂ in thesequence shown in FIG. 4. Then, the display value of the defocuseddegree detecting device varies according to the movement of lens barrel150. The driving action of the motor is brought to a stop when thedefocused state becomes an in-focus state. The motor driving action canbe controlled either automatically or manually. An automatic focusingoperation can be accomplished by automatically detecting the defocusingdegree and by automatically turning the motor on and off through thecontrol circuit. It goes without saying that, in accordance with theinvention, zooming can be accomplished either before or after focusing.

In the embodiment described above, the coil is wound on the moveableelement on the side of the focusing lenses. The same effect isobtainable, however, by winding the coil on the stator instead of themovable element in the same manner as in the case of the first movablering. In the case of FIG. 1, showing the arrangement of the invention byway of example, the stator for driving the variator lens group isdisposed on the upper side while the stator for driving the compensatorlens is disposed on the lower side and the arrangement thus consists oftwo seriated stators. However, the same effect can be obtained by usinga single stator as shown in FIG. 5 with an intermediate tap arranged topermit driving two movable elements. The movable element which serves asa movable ring may be formed into one unified body with the lens barrel.Such arrangement not only gives the same effect but greatly contributesto a reduction in cost.

While the linear step motor is employed in the embodiment describedabove, this may be replaced with a linear servo-motor to obtain the sameeffect.

As will be understood from the description of an embodiment given above,the advantages of the lens barrel according to the invention include:

(1) The provision of the linear step motor which also serves as a lensbarrel facilitates attaching and detaching the lens to and from acamera. This facilitates mounting arrangements of the lens barrel as aninterchangeable lens.

(2) Compared with the conventional arrangement of the external motortype, the invented arrangement dispenses with a reduction mechanism andthis results in a reduction in the number of assembly processes.

(3) Improvement in appearance because of compactness.

(4) With interlocking gears replaced by a direct connection arrangement,there is no play and forward and backward movements can be accomplishedwith a high degree of precision and improved responsivity.

(5) Driving can be accomplished at a high or low speed in proportion tothe frequency of the pulse signal. This permits speed variation over awide range.

(6) The use of a permanent magnet force gives a self retaining force,which ensures that a desired position can be retained without the use ofa brake.

(7) The lens barrel and the ferromagnetic member can be formed into oneunified shape. This permits a reduction in the number of parts.

(8) The stator element and the movable element of the linear step motortype electromagnetic mechanism can be placed within a space between thebase cylinder and the movable lens barrel of the lens barrel assembly.Therefore, the electromagnetic mechanism does not cause any particularincrease in the outside dimensions of the lens barrel assembly. Besides,unlike the conventional lens barrel of the type incorporating anelectric motor which results in some protrudent part on the outside ofthe lens barrel, the lens barrel according to the invention permits aphotographing operation without losing weight balance in thelongitudinal direction or the direction of the optical axis of the lensbarrel.

Further, in the embodiment shown in FIGS. 1-5, the linear step motor isarranged to move two lens barrels 106 and 139 for zoom lenses and isprovided with permanent magnets 201-201n as a stator of the fixed lensbarrel 102 with magnet parts 202 and 203 provided at the fore ends ofthe magnetic poles of each permanent magnet. Meanwhile, sliding members138 and 139 are provided with a plurality of pole teeth 206 (or teethA-I, ---) and are arranged in sequence along the optical axis as themovable element. However, the arrangement of the stator and that of themoveable element may be interchanged.

A second embodiment of the invention is as shown in FIGS. 6 and 7, theformer showing the lens barrel in a longitudinal sectional view and thelatter in a partially cutaway view, respectively. The lens barrel ofthis embodiment includes a lens optical system consisting of four lensgroups and a zooming mechanism.

Referring to FIGS. 6 and 7, the first lens group consists of lenses L1,L2 and L3. The second lens group, which is adapted for varying themagnification of an image, consists of lenses L4, L5 and L6. The thirdlens group, which is adapted for correcting image distortion resultingfrom the variating action of the second lens group on the magnification,consists of a lens L7. The fourth lens group, which is adapted forperforming a focusing action, consists of lenses L8, L9, L10, L11 andL12. In the preceding embodiment, shown in FIG. 1, the len opticalsystem comprises a relay lens group consisting of lens L1, L3 and L3,variator lens group L4-L6 and compensator lens group L7. The presentinvention, however, is also applicable to an optical system which isknown by the name of a single lens (a standard lens) consisting solelyof focusing lenses. The first lens group, L1-L3 is carried by lensbarrel 1, which is arranged to hold each lens in place, inside thereof,through lens holding members 1a and 1b. A second lens barrel 2 isconnected to the first lens barrel by means of screws 3.

A zoom mechanism is disposed within the second lens barrel. The rear endof the second lens barrel is formed into a flange, part 2a, whichprotrudes inward. At the fore end of the second lens barrel, a retainerplate 4 is fixedly interposed in-between the first and second lensbarrels, 1 and 2. Guide members 5 and 6, which are in a bar-like shape,are disposed to span the space between retainer plate 4 and theabove-stated flange part 2a, and are secured to them. On the innercircumference of the second lens barrel 2, there is fitted in acylindrical cam member 7 which is arranged to be rotatable by a rotatoryoperation of a zoom operation ring 14 which will be described later. Thecylindrical cam member is provided with cam slots 7a and 7b forcontrolling the movement of variator lens group L4-L6 and compensatorlens group L7. Variator lens group L4-L6 is carried by a lens holdingmember 8. Lens holding member 8 is connected to a movable member 9 whichis fitted on the above-stated guide member 5.

The above-stated movable member 9 has a guide pin 10 secured thereto.Guide pin 10 is fitted into the cam slot 7a which is provided in cammember 7 for controlling the variation of the magnification of theimage.

Compensator lens L7 is carried by a lens holding member 11 which isconnected to a movable member 12 fitted on the above-stated guide member6. This movable member 12 has a guide pin 13 secured thereto. Guide pin13 is fitted in cam slot 7b provided in cam member 7 for controlling thecorrecting action of compensator lens L7. The above-stated zoomoperation ring 14 is fitted on the outer periphery of second lens barrel2 and is connected to cam member 7 through a connecting means 15.

In the technical field of lens barrels, of the type arranged to becapable of performing a zooming action, many kinds of meanscorresponding to connecting means 15 have been proposed. Therefore, oneof such known means of the prior art may be employed as the connectingmeans 15. For example, the connecting means may be arranged as follows:zoom operation ring 14 and cam member 7 are connected with each other bya connecting member which pierces through a hole provided in thecircumference of second lens barrel 2. With the zoom lens arranged inthis manner, a rotation of zoom operation ring 14 around the opticalaxis 0₁ -0₂ causes cam member 7 to rotate together with ring 14. Withcam member 7 caused to rotate in this manner, the second and third lensgroups respectively move in parallel with the optical axis to perform amagnification varying action and a distortion correcting actionaccording to the degree of displacement of the curves of the cam slotsformed in the cam member.

A third lens barrel 16 contains an electromagnetic induction mechanismarranged to control the extent of the forward movement of the fourthlens group consisting of focusing lenses L8-L12. Since the third lensbarrel is arranged to form a part of the magnetic circuit which will bedescribed herein, the third lens barrel is made of a magnetic materialand is connected to the second lens barrel with screws 17.

A bayonet or screw mount member which is provided for mounting the lensbarrel assembly on the camera body is attached to a mount member 18.Mount member 18 is secured to the rear end of the third lens barrel 16with screws 19.

A cylindrical member 20 is secured to the inner circumferential face ofthe third lens barrel 16. This cylinder is made of a magnetic materialand is arranged to form a stator part. As shown in FIG. 8, cylindermember 20 is provided with arm parts 20A, 20B, --- which extend from theinner circumferential face of cylinder member 20. The fore end of eachof the arm parts is formed into teeth 20a₁, 20a₂, --- or 20b₁, 20b₂,---, and so on. These teeth are arranged to form a concentric circle.The arm parts of stator part 20 or the cylinder member are provided withexciting coils 21₁ -21₅ which are wound around them for the purpose ofexciting the teeth. Reference numeral 22 indicates a hollow cylindricalmember. Hollow cylindrical member 22 is arranged to serve as therotation shaft of the motor and is made of a magnetic material, such asferrite or some other suitable oxide magnetic material. On the outercircumference of this hollow cylindrical member 22 and around theoptical axis thereof, alternately arranged A and N poles are provided. Alens holding member 23, which is arranged to hold the fourth lens groupfor focusing, is secured to the inner circumferential face of hollowcylindrical member 22 by means of an adhesive or the like. The outerperipheral portions of lens holding member 23 at the fore and rear endsthereof are are formed into helicoidal screw parts 23a and 23b. Thethreads of these helicoidal screw parts 23a and 23b are engaged with thehelicoidal screw parts 16a and 16b which are formed on the flange parts(or protrudent parts) formed at two ends of the third lens barrel 16 toextend in the radial direction relative to the optical axis.

Coils 21, mentioned in the foregoing, are arranged to receive power froma power source which is not shown. For this purpose, an electricalconnector may be provided on mounting surface 18a, of mount member 18,of the above-stated mount lens of the lens barrel assembly. A connectorthus arranged may be connected to coils 21 thereby permitting powersupplied from a drive circuit, disposed on the side of the camera body,when the lens barrel assembly is mounted on the camera body. Another wayof supplying power to coils 21 is to use a battery which may be arrangedon the side of the lens barrel assembly to effect the power supplythrough electrical connections. When power is supplied to the terminalof the above-stated coil arrangement 21, cylinder member 20 becomes anelectromagnet thereby forming magnetic circuits at third lens barrel 16,cylinder member 20, permanent magnet cylinder member 22, lens holdingmember 23 and flange parts 16A and 16B formed at the fore and rear endsof the third lens barrel 16. This creates a rotational force to rotate,on the optical axis, a rotor consisting of permanent magnet cylindermember 22 and lens holding member 23. This rotating force causesfocusing lenses L6-L12 to move parallel to the optical axis through thescrewed engagement of lens holding member 23 and flange parts 16A and16B of the third lens barrel 16. Forward or backward movement of thefocusing lenses can be determined by selecting the direction of rotationof the rotor. This is accomplished by selecting the direction in whichthe power supply is connected to the driving circuit, which is not shownto the above-stated coil arrangement 21. Therefore, the direction of thefocusing lenses' motion is controllable by such selection.

In the rotor shown in FIG. 6 (consisting of hollow cylindrical member 22and lens holding member 23), the space between the rotor and the stator(or the cylinder member 20) must be arranged to be as small as possiblein order to ensure smooth movement of the rotor. In one example of amethod for attaining this purpose, lens retainer member 23 and flangeparts 16A and 16B are provided with bearing means. As this embodiment isdescribed above, the stator of the motor is arranged to be a fixed lensbarrel and the rotor thereof to be a hollow cylinder member. Opticalelements such as lenses are disposed within the hollow cylinder member.The optical elements are arranged to make controlled movements along theoptical axis of such elements. Then, a signal of an image formed by thefocusing optical system is supplied, for example, to a focus detectingdevice (including defocused degree detection means) which is arranged todetect whether the focusing optical system should be moved forward orbackward. The focusing optical system can then be moved as required forbringing it into an in-focus position through a coil power supplycircuit which is not shown.

In the embodiment described above, the coil is disposed on the side ofthe stator and the permanent magnet on the side of the rotor. The coil,however, may be disposed on the rotor side. Further, the arrangement maybe replaced with a cordless motor. It is also possible to have cylindermember 22, the rotor, formed into one unified body with lens holdingmember 23 during the molding process. Cylinder member 22 does not haveto be of a closed cylindrical shape but may be replaced with an arcuatepermanent magnet attained to the outer circumferential surface of thelens holding member. In the embodiment, focusing optical elements L8-L12are arranged to be movable, however, in accordance with the invention,this focusing optical system may be replaced with another optical systemarranged to have a part thereof attached to a fixed lens barrel whilethe rest is arranged to be movable in the direction of the optical axis.

In accordance with the invention, some components of the lens barrelassembly can be utilized as a rotor and as a stator of a motor. Thisremoves the need for arranging a driving motor and a gear mechanism, fordistance adjustment, on the outside of the lens barrel, as in the caseof the conventional arrangement, and yet, a photo-taking lens that iscompletely electrically controllable can be obtained. Further, inaccordance with the invention, the focusing optical system drivingmechanism can be arranged into one stator part and one rotor part.Therefore, it is possible to arrange the focusing optical system drivingmechanism into one unit and to have the unit placed within third lensbarrel 16. Then, in the processes of manufacture and productionmanagement, this unit can be processed separately from the zoommechanism part shown in FIG. 1 for the purposes of assembly, qualitycontrol and production control.

In accordance with the invention, the fixed member of the lens barrelassembly can be used as the stator and lens holding member 23 as a partof the rotor. This permits support for the lens holding member 23 to beprovided by parts (the flange parts 16A and 16B) of a fixed lens barrelfor simplification of the construction of the lens barrel assembly.

We claim:
 1. A lens barrel for performing rear-focusing, comprising:(a)a body tube; (b) zooming means, said zooming means having a zoom lenscontained in the interior of said body tube and zoom lens drive meansresponsive to actuation for moving said zoom lens to effect zooming; (c)a focusing lens arranged nearer to the body of a camera than said zoomlens; (d) electromagnetic induction means for controlling the movementof said focusing lens, said electromangetic induction means having acylindrical member carrying said focusing lens, made of magneticmaterial and provided with permanent magnet pieces on its outerperiphery; a plurality of arms radially positioned on the innerperiphery of said body tube, teeth formed in the free ends of said armsto confront said magnet pieces of said cylindrical member, excitingcoils turned around said arms; and rotational-to-axial transmittingmeans, said rotational-to-axial transmitting means having a malehelicoid formed in the outer periphery of said cylindrical member, and afemale helicoid fixed to the inner periphery of said body tube andmeshing with said male helicoid, whereby the cylindrical member iscaused to rotate by supplying power to the coils wound around the arms,and, due to the meshing of said female helicoid on said body tube andsaid male helicoid on said cylindrical member, this rotation of saidcylindrical member causes said cylindrical member to also move axiallyalong an optical axis of said lens barrel, thereby causing said focuslens carried by said cylindrical member to perform a rear-focusingoperation.